And when one congressman complained, the message from Paul’s camp was: too bad.

The Kentucky Republican has lent his name to fundraising pitches for the National Association for Gun Rights, a group that says the National Rifle Association is too willing to compromise on gun rights.

The group has blitzed the districts of Virginia Republicans Cantor and Rep. Scott Rigell with $50,000 worth of TV and radio ads accusing them of helping President Barack Obama pass gun control legislation.

Paul’s email pitches for the group don’t mention Cantor or Rigell by name, but his activity for an organization that attacks fellow Republicans shows the potential 2016 presidential contender isn’t afraid to pick a fight inside the party.

“Rand signs normal, run-of-the-mill activist emails and letters for numerous groups and this is one of them,” Stafford told POLITICO. “That’s all he’s ever done for them, he’s not affiliated with the group in any way, he doesn’t control how they decide their activism should take place in terms of who the people are that need to be shored up on an issue.”

Paul poses a formidable challenge for fellow Republican lawmakers. He has a built-in base of libertarians, and his profile rose again last month after he filibustered against the Obama administration’s drone policy and won the Conservative Political Action Conference presidential straw poll.

Rigell, a second-term congressman from Virginia Beach, reelected with nearly 54 percent of the vote, this year introduced a bipartisan bill to strengthen penalties for straw purchasers — those who knowingly buy guns for people who cannot pass a background check.

But he also has an A-minus rating from the NRA, and said the ads caught him by surprise, forcing him to air several radio spots of his own to refute their claims.

“I outright oppose any initiative that would directly or indirectly result in the creation of a national database of firearms and or firearm owners,” Rigell said in an interview. “Their charge that I am leading this, that I am supporting this, is an egregious lie, and completely unfounded.”

When he discovered that Paul was fundraising for the NAGR, he called the senator and Paul promised to investigate and get back to Rigell.

The congressman also sent Paul a two-page handwritten note asking him to repudiate the group.

“It is true your name is not on any email, direct mail piece, nor is it mentioned in the television or radio ads,” Rigell wrote, according to a copy of the letter viewed by POLITICO. “Yet it is also true, irrefutably, that your good name is being leveraged, with your permission one must assume, by a corrupt, detestable outfit.”

A day or so later, Stafford told Rigell’s office that nothing would be done, according to Rigell.

“The reply essentially was: ‘It’s between you and this group and the senator will not disassociate himself from that organization.’ Which surprised me,” Rigell said.

Paul has signed emails and letters supporting NAGR efforts primarily against congressional gun control bills and the United Nations small arms treaty for about two years, Stafford said.

Stafford said that Paul’s office was previously unaware of the ads against Cantor and Rigell. It only found out about the Rigell ads from the congressman and about the Cantor ads when asked by POLITICO.

Cantor’s office declined to comment for this story.

Of course, there are several conservative groups that target sitting Republicans, such as the Club for Growth, that go after incumbents or candidates they don’t feel are conservative enough.

Republican members often support these groups, and according to Rigell, that’s just fine.

The situation with Paul, he says, is different.

“I expect and welcome efforts by others or organized groups to hold me accountable for votes I’ve cast and positions I advocate for,” Rigell said. “This is a reasonable expectation and an essential part of good governance.

“This situation is in stark contrast to that,” he said. “They are lying about who I am, and so for a senior Republican to saddle up with a group like that and with the money Rand Paul raises, he is providing the mechanism by which these ads are launched. So he is as responsible as they are for these false attacks.”

Paul’s refusal to rebut the group shows something about his character, Rigell said.

“At the beginning, what was going on showed a lack of judgment on behalf of Sen. Paul, but now that he’s chosen to do nothing about this, it is a reflection of his character,” he said.

Rigell said he reached out to NAGR Executive Director Dudley Brown several times with no success. In addition to the advertising, Brown has held two news conferences in Rigell’s district and one in Cantor’s.

Brown and the NAGR did not respond for a request for comment for this story.

The NAGR ads accuse Cantor, who has an NRA “A” rating, of “wanting to pass Obama’s gun control schemes.”

In the ad, a narrator says he “doesn’t sound like a Virginian or a Republican anymore; Eric Cantor sounds like someone else,” as a graphic of Cantor’s face morphs into Obama’s.

In February, Cantor suggested on CNN that a beefed-up database for background checks, implemented in Virginia after the Virginia Tech shooting, could serve as a national model.

The strong NRA ratings for Cantor and Rigell don’t impress NAGR — the group has accused the top gun rights organization of “signaling surrender on handing President Obama and his anti-gun pals more information about American gun owners.”

The NRA did not respond to a request for comment.

Meanwhile, Paul continues to solidify his standing as a strong pro-gun-rights Republican. He has already promised to filibuster Democratic gun control legislation that would broaden background checks and crack down on interstate gun trafficking.

And Paul’s support appears to have helped NAGR attract new members. In fact, one of them was David Rigell, the congressman’s brother. But then he saw what the group was saying.

“He was very surprised to see my name as a member of Congress who was being vilified by the email,” Rep. Rigell said. “He mentioned to me that the reason he had joined this organization was because of a direct solicitation he received from the group that was from Rand Paul.”